WEDNESDAY, Feb. 26, 2014 (HealthDay News) -- Four out of five teens suffering from juvenile fibromyalgia will continue to have pain and other symptoms in adulthood, a new study finds.

About half of these children will end up as grown-ups with full-blown adult fibromyalgia, the researchers found.

"Half of the former teens we studied met the full criteria for adult fibromyalgia, and another 35 percent of them continued to have symptoms of fatigue, pain and sleep difficulty, but did not meet all the criteria for fibromyalgia syndrome," said study author Susmita Kashikar-Zuck, research director in behavioral medicine and clinical psychology at Cincinnati Children's Hospital Medical Center.

The study, published in the March print issue of Pediatrics, stemmed from research into juvenile fibromyalgia, Kashikar-Zuck said.

Fibromyalgia is a mysterious disorder that causes muscle pain and fatigue. People with the syndrome complain of sensitive places in their body that hurt when pressure is applied.

"It appears to be caused by a pain hypersensitivity in the central nervous system," Kashikar-Zuck said. "It's sort of like the volume is turned up on pain, and now they are exquisitely sensitive to pain."

Doctors aren't certain what causes fibromyalgia, although genetics may play a role. "Many of the children we see who have fibromyalgia have a parent with fibromyalgia," Kashikar-Zuck noted.

Between 80 percent and 90 percent of fibromyalgia patients are female, according to the U.S. National Institutes of Health.

Juvenile fibromyalgia can drastically affect a teen's life, causing missed school days and withdrawal from social activities, Kashikar-Zuck said.

Researchers wondered if these problems continued into adulthood, and decided to follow a group of 94 teenagers with juvenile fibromyalgia for six years. The teens were diagnosed with the disease between 2002 and 2010, with an average age at diagnosis of 15.

The study authors found that 51 percent of the patients, now young adults with an average age of 21, continued to have symptoms that meet the American College of Rheumatology's criteria for adult fibromyalgia.

More than one-third did not meet the standards for a full diagnosis but still complained of specific symptoms related to fibromyalgia. These included pain, fatigue and difficulty sleeping.

When compared to healthy young adults their age, the patients who had experienced juvenile fibromyalgia reported significantly higher pain, poorer physical function, greater anxiety and more visits to the doctor.

Dr. Anne Eberhard, a pediatric rheumatologist at Cohen Children's Medical Center of New York in New Hyde Park, said these results make sense given the major role that stress plays in fibromyalgia.

"It is not surprising that the symptoms are still seen and persist into early adulthood, where major life decisions are being made," Eberhard said.

The study also found that juvenile fibromyalgia patients were more likely to be married as young adults compared with healthy folks their age, but were less likely to have attended college. About 62 percent had attended some college or obtained a degree, compared with 76 percent of the healthy control group.

While these findings could seem discouraging for juvenile fibromyalgia patients, Eberhard said one can look at the glass as being half-full rather than half-empty.

"Nearly half of the originally diagnosed patients with fibromyalgia were improved to the point that they no longer fulfilled the diagnostic criteria for fibromyalgia. Many of the patients in the study with fibromyalgia were attending college and indeed some had married and even given birth," she said.

"This is very encouraging as despite having more pain than the controls, these patients were able to lead a normal, productive life," she added.

Even more encouraging is the fact that fibromyalgia treatment options have improved in recent years, particularly for adults, said Dr. Lucinda Bateman, founder of the Fatigue Consultation Clinic in Salt Lake City, Utah.

The U.S. Food and Drug Administration has approved antidepressant and anticonvulsant medications for adult fibromyalgia, and cognitive behavioral therapy -- a type of mental health counseling -- can be useful in helping patients better cope with their pain. Physical activity also has proven effective in controlling symptoms, the study says.

"It doesn't surprise me that many still have the symptoms, but it appears they do have a better chance of moving through it," Bateman said.

The study does emphasize the importance of properly diagnosing juvenile fibromyalgia, Bateman and Kashikar-Zuck said.

"Parents need to be careful about differentiating growing pains with fibromyalgia," Kashikar-Zuck said. "If they see a child who also has chronic muscle pain but also sleeplessness, they should seriously consider whether an evaluation should be done for fibromyalgia."